利用标量解法，导出了弱导阶跃光纤线偏振模(LPmn)的场分布和LPmn混合模式的光强表达式。结果表明，低阶LPmn模的模场范围均随纤芯半径的增加而增大，随纤芯折射率的增加而缩小，随包层折射率的增加而扩大；随传输距离和模式混合份额的增加，LPmn混合模式的光强减少；非相干混合模的M2因子随高阶模式光强所占分额的增加而逐渐变大，M2并非一直随纤芯半径的增加而增大，存在着一个临界值a=30 μm。

Using the scalar method, the field distribution of the linear polarization in a step-index of weakly guiding and the hegeneral expression of the mixed modes are derived. The results show that, the mode field ranges of the lowed LPmn increases with the fiber core radius and the coating layer index. The mode field ranges of the lowest order LPmn modes reduces with the increase of the fiber core index. The optical strength of the mixed modes reduces with the increase of the transmission distance and the proportion of mixed modes. The M2 factor of the uncoherent mixed modes increases gradually with the increase of the proportion of the highest order LPmn modes. Howerer, the increase of M2 factor approaches a critical value when the fiber core radius is a=30 μm.